Lead wire for fluorescent lamps



Feb. 20, 1951 L. R. PETERS 2,542,352

LEAD WIRE FOR FLUORESCENT LAMPS Filed June 10, 1947 Invenfirov: Leo R.Pefirers,

His A h' rovneg Patented Feb. 20, 1951 LEAD WIRE FOR FLUORESCENT LAMPSLeo R. Peters, Cleveland Heights, Ohio, assignor to General ElectricCompany, a corporation of New York Application June 10, 1947, Serial No.753,764

Claims. (Cl. 176-126) My invention relates to electric gaseous dischargelamps, and more particularly to fluorescent lamps.

An object of my invention is to reduce the end discoloration whichnormally occurs in such lamps in the form of dark deposits near the endsof the lamps adjacent the electrodes. Other objects are to improve themaintenance and efliciency of such lamps. Further objects and advantagesof my invention will appear from the following description of speciesthereof.

In the drawing, Fig. 1 is an elevation of a lamp comprising myinvention, and Fig. 2 is a perspective view, on an enlarged scale, ofthe mount structure at each end of the lamp.

Referring to the drawing. the lamp shown therein is generallyrepresentative of the wellknown fluorescent lamps of low pressuremercury vapor positive-column type. The lamp comprises an elongatedtubular envelope l of glass or the like having on its interior surface acoating 2 of fluorescent material such as manganese-activated zincberyllium silicate or magnesium. tung tate or mixtures thereof. The endsof the envelope are sealed by mounts such as shown in Fig. 2 and eachcomprising a stem 3 through which extend lead-in wires 4-4 between whichis mounted a thermionic activated electrode 5 which may be a coiled orcoiled-coil filament of tungsten coated with an electron emissivematerial, such as one or more of the oxides of alkaline earth metalslike barium or strontium. One of the stems 3 may be provided with theusual exhaust tube 6. The envelope may be filled with a rare gas at apressure 01' a few millimeters, for example argon at about 2 to 5 mm.pressure, and a small amount of mercury 7. Such lamps are ordinarilyoperated at a current density such as to result in a mercury vaporpressure of the order of magnitude 01' microns.

As pointed out above, during the operation of such lamps dark depositsare formed on the normally white fluorescent powder 2 on the interioroi. the envelope l adjacent the electrodes 5, 5. According to thepresent invention, such discoloration is appreciably reduced byconstituting at least the surfaces of the portions of the leadin wires4, within the envelope I, of metallic aluminum.

Each of the lead-in wires 4 usually consists of three sections,including an outer lead 8 usually of copper, a short press lead 9consisting of a copper-sleeved nickel-iron core, and an inner lead It.The inner leads ID are here shown as of the form disclosed and claimedin the Flaws Patent 2,312,245 which is assigned to the same assignee asthe present case, wherein intermediate portions of the leads are shapedto form hooks ll clamped around the ends of the filamentary cathode 5and the extremities of the leads are bent to extend parallel to thecathode to constitute anode portions I2.

In accordance with my invention, the entire surface of each of the innerleads I 0 may be provided with a coating or covering [3 of metallicaluminum (indicated by dotted lines), for example a coating of aluminumpaint, or of electrolytically plated aluminum. The base or core wire ofsaid inner leads may consist of a suitable metal or alloy such as ironor nickel, although the presently preferred material is deoxidizedcopper. Alternatively, the inner leads 10 may be made of solid aluminumalthough at present I prefer the abovementioned construction sincealuminum wire is somewhat difficult to worl: with.

A thin coating l3 of aluminum may be applied to the inner leads I0 priorto assembly of the then straight composite lead wires 4, 4 into the stem3, by dipping the inner lead portions l0 into a bath of aluminum paintconsisting, for example, of 325 mesh degreased aluminum powder in asolution of nitrocellulose in amyl acetate. The thin coating of aluminumpaint does not interfere with the operation of the automatic stemmakingand mount-making machines ordinarily used in the manufacture of themount shown in Fig. 2. The binder in the aluminum paint is in this caseburned out during the course of manufacture of the stem and lamp. Insome cases where the stem and lead wires are assembled by a processinvolving excessive heating of the inner leads l0, it may be desirableto brush the aluminum paint on the said inner leads after such assemblyhas been made, in order to avoid a reaction between the aluminum and thecore or base metal (copper, for instance) of the said inner leads.

In comparative tests, lamps with aluminumcoated iron inner leads showedsubstantially less end discoloration and longer life (from 10-50%) thanlamps with bare iron inner leads. The aluminum-coated lead wire lampsalso had a higher efficiency of 2.8 lumens per watt which persistedthroughout lamp life. In another test, lamps with aluminum-dipped andaluminumelectroplated copper inner leads both gave longer life thanlamps with bare nickel leads. On the other hand, I found that coatingthe inner leads with alundum (A1203) resulted in excessive etching ofthe cathode on cold starting of the lamps. Moreover, coatings ofmagnesium, in place of aluminum, resulted in very bad discoloration atthe ends of the lamp.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A fluorescent electric discharge lamp comprising a sealed tubularglass envelope having a coating of fluorescent material on the interiorthereof and containing an ionizable atmosphere including mercury vapor,a glass stem sealed to each end of said envelope, composite multisectionlead-in wires projecting into said envelope through said stems and eachhaving an intermediate seal section thereof fused in one of said stemsand an outer section projecting exteriorly of the envelope and an innersection projecting interiorly of the envelope, filamentary electrodesmounted on and electrically connected to the said inner portions of thelead-in wires at respective ends of the envelope and having thereon anelectron emissive coating of alkaline earth oxides. the intermediatesections of said lead-in wires being constituted of copper-cladnickel-iron wire,

the said inner sections only of said lead-in wires having at least thesurface layer thereof constituted of metallic aluminum which serves tominimize the formation of dark deposits on the fluorescent coating atthe ends of the envelope during operation of the lamp.

2. A fluorescent electric discharge lamp comprising a sealed tubularglass envelope having a coating of fluorescent material on the interiorthereof and containing an ionizable atmosphere including mercury vapor,a glass stem sealed to each end of said envelope, compositemulti-section lead-in wires projecting into said envelope through saidstems and each having an intermediate seal section thereof fused in oneof said stems and an outer section projecting exteriorly of the envelopeand an inner section projecting interiorly of the envelope, filamentaryelectrodes mounted on and electrically connected to the aid innerportions of the lead-in wires at respective ends of the envelope andhaving thereon an electron emissive coating of alkaline earth oxides,the intermediate sections of said lead-in wires being constituted ofcopper-clad nickel-iron wire, the said inner sections only of saidlead-in wires consisting of a base metal wire covered with metallicaluminum which serves to minimize the formation of dark deposits on thefluorescent coating at the ends of the envelope during operation of thelamp.

3. A fluorescent electric discharge lamp compriing a sealed tubularglass envelope having a coating of fluorescent material on the interiorthereof and containing an ionizable atmosphere includin mercury vapor, aglass stem sealed to each end of said envelope, composite muiti-sectionlead-in wires projecting into said envelope through said stems and eachhaving an intermediate seal section thereof fused in one of said stemsand an outer section projecting exteriorly of the envelope and an innersection projecting interiorly of the envelope, filamentary electrodesmounted on and electrically connected to the said inner portions of thelead-in wires at respective ends of the envelope and having thereon anelectron emissive coating of alkaline earth oxides, the intermediatesections of said lead-in wires being constituted of copper-cladnickel-iron wire. the said inner sections only of said lead-in wiresconsisting of a base metal wire of copper covered with metallic aluminumwhich serves to minimize the formation of dark deposits on thefluorescent coating at the ends of the envelope during operation of thelamp.

4. A fluorescent electric discharge lamp comprising a sealed tubularglass envelope having a coating of fluorescent material on the interiorthereof and containing an ionizable atmosphere including mercury vapor,a glass stem sealed to each end of said envelope, compositemulti-section lead-in wires projecting into said envelope through saidstems and each having an intermediate seal section thereof fused in oneof said stems and an outer sectionproiecting exteriorly of the envelopeand an inner section projecting interiorly of the envelope, filamentaryelectrodes mounted on and electrically connected to the said innerportions of the lead-in wires at respective ends of the envelope andhaving thereon an electron emissive coating of alkaline earth oxides,the intermediate sections of said lead-in wires being constituted ofcopper-clad nickel-iron wire, the said inner sections only of saidlead-in wires consisting of a base metal wire of iron covered withmetallic aluminum which serves to minimize the formation of darkdeposits on the fluorescent coating at the ends of the envelope duringoperation of the lamp.

5. A fluorescent electric discharge lamp comprising a sealed tubularglass envelope having a coating of fluorescent material on the interiorthereof and containing an ionizable atmosphere including mercury vapor,a glass stem sealed to each end of said envelope, compositemulti-section lead-in wires projecting into said envelope through saidstems and each having an intermediate seal section thereof fused in oneof said stems and an outer section projecting exteriorly of the envelopeand an inner section projecting interiorly of the envelope, filamentaryelectrodes mounted on and electrically connected to the said innerportions of the lead-in wires at respective ends of the envelope andhaving thereon an electron emissive coating of alkaline earth oxides,the intermediate sections of said lead-in wires being constituted ofcopper-clad nickeliron wire, the said inner sections only of saidlead-in wires consisting of metallic aluminum which serves to minimizethe formation of dark deposits on the fluorescent coating at the ends ofthe envelope during operation of the lamp.

LEO R. PETERS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Atchley Apr. 14, 1942

